Tube heating furnace



May 28, 1968 R. M. BRECKENRIDGE 3,385,269

TUBE HEATING FURNACE Filed Jan. 26, 1967 FIG INVENTOR. R. M.BRECKENRIDGE ATTORNEY.

United States Patent O 3,385,269 TUBE HEATING FURNACE Robert M.Breckenridge, Maple Glen, Pa., assignor to Selas Corporation of America,Dresher, Pa., a corporation of Pennsylvania Filed Jan. 26, 1967, Ser.No. 611,856 7 Claims. (Cl. 122-240) ABSTRACT F THE DISCLOSURE Almultiple cell tube heater in which one cell is used to bring the tiulidbeing heated almost to iinal temperature and a second :cell is used tofinish the heating. Said one cell Lis fired primarily with oil as a fuelwith gas fuel being used to supplement the oil. The second cell is firedentirely by gas as a fuel to `get accurate temperature control.

Background of invention In the heating of various uids in thepetrochemical industry, it is customary to pass the fluid through anelon gated, serpentine coil, the passes of which may be eitherhorizontal or vertical. In heating the liuid as it flows through thecoil it is desirable, if not necessary, to raise the temperature at Iapredetermined rate and to control accurately the final or exittemperature of the uid. Furnaces of this type are usually red witheither oil or gas as the fuel. Generally speaking more accurate controlof the temperature along the coil ycan be obtained with gas as a fuel,and for this reason it is often used even though it is more expensivethan oil. In some places, however, even though `accurate control isneeded, gas is not available in sufficient quantities and/or its cost istoo high to be used in the quantities necessary to tire a large tubeheater.

Summary ofthe invention The furnace or heater of the present inventionis provided with a plurality of chambers that are substantiallyseparated from each other. An elongated, serpentine coil with verticallyextending tube passes is suspended in the furnace with one group of tubepasses in one chamber |and -other passes in another chamber. The chambercontaining that portion of the coil forming the first passes throughwhich the fluid to be heated flows, is ired primarily with oil as afuel. Gas supplementary heating is used in this chamber to even out thetemperature of the tube passes lengthwise. The chamber containing thelast Ifew tube passes through which the fluid being heated travels, isheated by gas burners which may be adjusted to control accurately thefinal temperature of the uid. If desired, the heater rnay be soconstructed that it contains more than one heating coil.

It is an object of the invention to provide a tube heater in which oilis the fuel use-d for the bulk of the Iheating Iand |in which gas isused to even the heating and produce the nal desired temperature of thematerial being heated.

It is la further object of the invention to provide a tube heater inwhich different sections of the coil are segregated so that they may beheated at different rates. Another object of the invention is to providean oil red tube heater having supplementary gas firing for accuratetemperature control.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to land forming apart of this specification. For a better understanding of the invention,however, its yadvantages and specific objects attained with its use,reference should be had to the accompanying drawings ice and descriptivematter in which I have illustrated and described Ka preferred embodimentof the invention.

In the drawings:

FIG. 1 is an elevation in section of the furnace taken on line 1-1 ofFIG. 2; and

FIG. 2 is a section with a portion taken on the upper line of 2-2 ofFIG. 1 and a portion taken on the lower line of 2 2 of FIG. l.

Referring to the drawings, it will be seen that while the he-ater may bebuilt in two sections, it is shown herein las being built in threesections including end chambers 1 and 2 and a center chamber 3. The endchambers are identical in construction and same reference numerals willbe used for the similar parts of these chambers. Each chamber includesan end wall 4 with lower side walls 5 and 6 joined by sloping walls 7and S to upper side walls 9 and 11. A floor 12 extends between the lowerends of lside walls S and 6 and beneath the center chamber. It wiill beseen that the lower portion of the chamber 1 is considerably wider thanthe upper portion. This is because the lower portion 'is fired with oilWhereas the upper portion is fired with gas.

Floor 12 is provided with a plurality of openings 14 on each sidethereof into which exten-d oil burners 15. These burners are supplied bya pipe 16 having a valve 17 therein. Supplemental -heat `for the upper,narrow p0rtion of the chamber is provided by Ia plurality of verticallyextending rows of gas burners 18, each row of which is supplied withfuel by a manifold 19. Valves 21 are provided so that each burner can beadjusted individually and each manifold has in it a valve 22 so that themanifolds can be adjusted individually after the burners have beenadjusted. lilii Central chamber 3, between the two end chambers, is of awidth throughout its height substantially equal to the width of theupper narrow portion of the end chambers. This central chamber isprovided with side walls 23 and 24 that extend vertically and areparallel to each other. There may also be provided, pairs of bafes 25which extend inwardly from the side walls between the end chambers andthe central chamber. These baies reduce the flow of combustion gasesbetween the chambers but do not close the chambers off completely fromeach other.

The central chamber 3 is heated by gas burners 26 which are placed invertical rows in the side walls. Each vertical row of burners issupplied with fuel from a manifold 27 and there are provided valves 28between the manifold and each burner. Suitable valves are also providedfor each manifold. It is noted that the gas burners in the upperportions of the side walls of the end chambers, as well as those in thewalls of the central chamber, are preferably of the radiant cup type.

The products are combustion produced by the burners in the variouschambers are carried off to a stack through an opening 31 that extendsfrom one side of the roof 29 from all three of the chambers. The roof isprovided with a vertically disposed and horizontally extending slot 32through which the coils to be heated are placed and are supported. Theheater of the present application is shown as being provided with twotube coils 33 and 34. One of these coils is in chamber 1 with its lastfew tube lengths in chamber 3 while the other coil 35 is located mainlyin chamber 2 with the last few tube lengths in chamber 3. Each of thecoils is a serpentine, endless coil consisting of vertically extendingtube passes that are joined at each end by return bends. In mounting thecoils in the furnace they are moved in a vertical position by a suitablecrane downwardly through slot 32. The lower retu-rn bends 36 areprovided with a threaded bolt 37 that extends through the iloor and isheld in position by nuts 38. Thus, the tube passes are definitelylocated in the furnace with respect to the burners and are held inposition. The upper ends of the coil are mounted so that, as the furnaceis heated, expansion of the tubes may take place. To this end, each ofthe upper return bends is provided with a bracket 39 through whichextends a ring 41. This ring has attached to it a cable 42 passing overpulleys 43 to a suitable counterweight 44. The counterweight ispreferably of a weight sufficient to equal about 60% of the weight ofthe pair of vertical tubes to which it is attached. In this manner, thetubes are held straight as they expand when the furnace is heated. Thereare provided bricks 45 which surround the tubes in slot `32 in order toclose this slot and prevent loss of heat therethrough. The space abovethe bricks 45 around the upper return bends and between beams 45 ispreferably filled with a fibrous insulation in order to insulate theroot of the heater.

ln operating the heater, the fluid to be heated, which can be naphtha orsome other hydrocarbon, is introduced at the bottom, fixed ends of coils33 and 34 in the last tube adjacent to the end walls 4 of chambers 1 and2 as indicated by the arrows. The flow is toward the center of theheater to be discharged at the fixed lower end of the last tube of eachcoil in the center of chamber 3, as indicated by the arrows.

Oil burners 1S are red in the lower portions of chambers 1 and 3 to-heat the side walls of those chambers to incandescence and therebyradiate heat to the lower ends of the tubes therein. The burners are sofired that the tubes are heated as evenly as possible. The hot productsof combustion owing upwardly through the narrow portions of thesechambers -heat the upper ends of these tubes, but not as much as thelower ends are heated. Supplemental heat to even out the temperature ofthe upper ends of the tubes is supplied by gas burners 18. Generally thelower burners will be supplied with less fuel than the upper burners ofeach row since the combustion gases passing through the lower part ofthe narrow section are hotter than those passing through the upper part.Individual burners and rows of burners can be adjusted as necessary.

By the time the fluid in the coils has reached the last few tubes incenter chamber 3 it has almost reached its final temperature, which mustbe accurately controlled. These tubes are in narrow chamber 3 betweenthe vertical rows of burners 26. The plurality of burners in each rowand the plurality of rows of burners can be adjusted -to regulateaccurately the nal temperature of the tubes and the fluid flowingthrough them.

Many tube heaters are fired entirely by oil, and adequate temperaturecontrol can be obtained for many noncritical processes. It is wellknown, however, that multiple radiant gas burners are capable of heatinga tube more uniformly and more accurately than is possible with oil. Thefurnace construction disclosed herein uses oil fuel to provide most ofthe heat and uses gas to supplement the oil in order to even out thetube temperatures and to control accurately the final temperature.Generally about 60% of the required heat is produced by the oil,although this percentage may be reduced somewhat Where the lrequirementsfor accurate control of the temperature of the tubes is increased.

While in accordance with the provisions of the statutes I haveillustrated and described the best form of embodirnent of my inventionnow known to me, it will be apparent to those skilled in the art thatchanges may be made in the form of the apparatus disclosed withoutdeparting from the spirit and scope of the invention set forth in t-heappended claims, and that in some cases certain features of my inventionmay be used to advantage without a corresponding use of other features.

What is claimed is:

1. In a tube heater the combination of structure forming a plurality ofvertically extending chambers communicating with each other, a first ofsaid chambers having a wide portion and a vertically displaced narrowportion, a plurality of oil burners tiring into said wide portion withthe products of combustion tiowing through said narrow portion, aplurality of gas burners firing into said narrow portion, meansindividually to adjust said gas burners, a second of said chambers beingof a width substantially equal to the width of the narrow portion ofsaid first chamber, a plurality of vertically extending rows of gasburners firing into said second chamber, 4an elongated serpentine coilcomprising a plurality of tubes connected by upper and lower returnbends, means to mount said coil with the tube passes extendingvertically through the center of said chambers with some of the tubepasses in said first chamber and some of the tube passes in said secondchamber.

2. The combination of claim 1 in which said structure includes a doorand a roof for said chambers, said roof being provided with a :slotextending above said chambers, said lower return bends being fastened tosaid door in spaced relation thereto, said upper return bends extendingthrough said slot, and means to bias said upper return ybends in anupwardly direction.

3. The combination of claim 1 in which said oil burners fire throughsaid door generally toward the portion of said structure forming sidewalls of the wide portion of said first chamber thereby to heat thelength of said tubes in said portion, the products of combustion-iiowing througs said narrow portion to heat the length of tubestherein.

4. The combustion of claim 3 including means to adjust the supply offuel t-o the gas burners in the walls of the narrow portion of saidfirst chamber to supplement the heating of the length of tubes thereinwhereby to even the heating of the entire lengths of the tube passes insaid first chamber.

`5. The combination lof claim 1 in which said gas burners firing intothe narrow portion of said first chamber are located in verticallyspaced rows, parallel to said tubes, in the structure forming the sidewalls of said narrow portion.

`6. The combination of claim 5 including means to adjust separately thesupply of gas to the rows of burners firing into said narrow portion ofsaid first chamber, and means to adjust individually the burners in each`now.

l. The combination of claim 1 in which the tube passes in said firstchamber form the entrance end of said coil and the tube passes in saidsecond chamber form the exit end of said coil, said vertical rows ofburners firing into said second chamber being parallel to and onopposite sides of the tube passes therein, and means individually toadjust said rows of burners.

References Cited UNITED STATES PATENTS 2,638,879 5/1953 Hess 122-356`3,066,656 12/ 1962 Hensel 122-240 3,182,638 5/ 1965 Lee et al. 122-2403,240,204 3/ 1966 Von Wiesenthal 122-240X CHARLES I. MYHRE, PrimaryExaminer.

